The present invention relates to a lapping control sensor used in controlling a height of a magnetoresistive effect (MR) head (MR height) when the MR head is fabricated, to a lapping control method using the sensor and to a manufacturing method of the sensor.
The MR height of a plurality of MR heads is collectively controlled by lapping one surface (ABS, Air Bearing Surface) of each bar obtained by cutting each row from a wafer so that the plurality of MR heads are aliened in one row. To control the mutual MR height of the plurality of MR heads of a bar and the mutual MR height of the MR heads of a plurality of bars to a corrective value, there are usually provided a plurality of lapping control sensors called as an electric lapping guide (ELG) or a resistance lapping guide (RLG) which detects the height of a lapped ABS surface, in each bar. The lapping of the ABS surface can be controlled in response to electric signals from the ELGs or RLGs.
Each of the ELGs or RLGs is mainly composed of a resister which is adjacent to the ABS surface to be lapped and extends in parallel. The ELG or RLG teaches an amount of lapping by changing its terminal voltage or its resistance due to the reduction of the height of the resister polished with polishing of the MR height. Such ELG with respect to the throat height of a magnetic pole gap in an inductive head, not to the MR height, is known by, for example, U.S. Pat. No. 4,689,877 and Japanese Unexamined Patent Publication No. 63(1988)-191570.
In manufacturing the MR head, the ELG or RLG is generally formed in the same process of manufacturing the MR head so as to have the same layered structure as that of the MR head. FIG. 1 shows a multi-layered structure of a conventional ELG or RLG. As shown in the figure, the conventional ELG or RLG has a multi-layered structure consisting of a metallic layer (shield layer) 10, an insulation layer (shield gap layer) 11, a resister layer (MR layer) 12 and lead conductors 13 and 14, which are made of the same material and layer thickness as those of the MR head.
Recently, in order to increase the bit density in a magnetic disk unit, narrower gap of the MR shield has been demanded. In order to make the shield gap narrower, it is necessary to decrease the thickness of the MR layer and/or the thickness of the shield gap insulation layer. However, there is a limit in decreasing the layer thickness of the MR layer because the characteristics of the head will be deteriorate. Thus, the thickness of the shield gap insulation layer sandwiching this MR layer has to be decreased. When the thickness of the shield gap insulation layer in the MR head is decreased, thickness of the insulation layer 11 in the ELG or RLG is also decreased as well.
When the thickness of the insulation layer 11 of the ELG or RLG is decreased as mentioned above, a short circuit may be formed temporarily between the lead conductors 13 and 14 via the metallic layer 10 and smears 15 (burrs) which may be protruded from the metallic layer 10 during the lapping control of the MR height. The smear metals 15 produced on the lapped surface of the metallic layer 10 are extended across the insulation layer 11 to contact the lead conductors 13 and 14 when the lapping direction is a direction of an arrow shown in FIG. 1, resulting in forming the electric short circuit between the metallic layer 11 and the lead conductors 13 and 14. When the short circuit is formed, resistance between the terminals of lead conductors 13 and 14, which is an ELG or RLG detecting output, is temporarily decreased and generates many noises in signals, resulting in that lapping for controlling of the MR height cannot be carried out.
In order to prevent the production of metallic smears when lapping the metallic layer, it may be considered to provide no metallic layer as an under layer of the ELG or RLG. However, if the resistor layer of the ELG or RLG has no under layer, it cannot have the same resistive change characteristics as the MR layer of the MR head due to differences between surface characteristics such as unevenness of the under layer. In order to enhance the controllability of the MR height, it is desirable that the resistor layer of the ELG or RLG and the MR layer of the MR element have the same resistive change characteristics.
In order to prevent the production of metallic smears when lapping the metallic layer, it is also considered that a lapping direction is set in the opposite direction to the direction of the arrow in FIG. 1. However, when the lapping direction is reversed, a recession between a substrate (slider) and an under film formed thereon becomes remarkably large causing the characteristics of the MR head itself to greatly deteriorate.
It is therefore an object of the present invention to provide a lapping control sensor which can securely and stably control a MR height of a MR head to a correct value.
It is another object of the present invention to provide a lapping control method using the sensor and a manufacturing method of the sensor.
According to the present invention, a lapping control sensor for a MR head, including a multi-layered structure of a metallic layer, an insulation layer, a resister layer and a lead conductor layer, and being provided in parallel with the MR head which has a multi-layered structure of at least a lower shield layer, a shield gap insulation layer, a MR layer and a lead conductor layer is provided. The insulation layer of the lapping control sensor has a thickness larger than that of the shield gap insulation layer of the MR head. The thickness of the insulation layer of the sensor is 0.1 xcexcm or more.
Also, according to the present invention, a lapping control sensor for a MR head, including a multi-layered structure of a metallic layer, an insulation layer, a resister layer and a lead conductor layer, and being provided in parallel with the MR head which has a multi-layered structure of at least a lower shield layer, a shield gap insulation layer, a MR layer and a lead conductor layer. The metallic layer, the insulation layer, the resister layer and the lead conductor layer of the sensor are made of the same material as that of the lower shield layer, the shield gap insulation layer, the MR layer and the lead conductor layer of the MR head, respectively. The insulation layer of the lapping control sensor has a thickness larger than that of the shield gap insulation layer. The thickness of the insulation layer of the sensor is 0.1 xcexcm or more.
Since an insulation layer of the lapping control sensor is formed so as to have a thickness of 0.1 xcexcm or more which is thicker than the thickness of a shield gap insulation layer of the MR head, noise generation due to the metallic smears can be prevented. Accordingly, the MR height can be securely and stably controlled to a correct value.
According to the present invention, furthermore, a lapping control method using the above-mentioned sensor is provided. In this method, the lapping control of a height of the MR layer of the MR head is executed in response to a signal from the lapping control sensor.
According to the present invention, also, a method for manufacturing a lapping control sensor is provided. This method includes the steps of sequentially depositing a metallic layer and an insulation layer at a position in parallel with a MR head during depositing steps of a lower shield layer and a shield gap insulation layer of the MR head, in which the insulation layer of the sensor has a thickness larger than that of the shield gap insulation layer and the thickness of the insulation layer of the sensor is 0.1 xcexcm or more, and sequentially depositing a resistor layer and a lead conductor layer on the insulation layer during depositing steps of a MR layer and a lead conductor layer of the MR head.
It is preferred that each of a plurality of lapping control sensors is located near the respective MR heads.
It is also preferred that the metallic layer, the insulation layer, the resister layer and the lead conductor layer of the sensor are made of the same material as that of the lower shield layer, the shield gap insulation layer, the MR layer and the lead conductor layer of the MR head, respectively.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.